1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Description of the Related Art
Various technologies have been developed for converting automotive exhaust gases. However, with ever-growing traffic volumes, emission control measures currently being taken are hardly enough. In Japan and throughout the world, automotive emission control is expected to become stricter. Especially, regulation of NOx in diesel exhaust gases is becoming very strict. Conventionally, NOx reduction has been achieved by controlling combustion systems of engines. However, it is no longer possible to sufficiently reduce NOx solely by controlling combustion systems. To cope with this problem, a Nox conversion system (called a urea selective catalytic reduction (SCR) system) using ammonia as a reducing agent has been proposed as a diesel NOx conversion system. In the urea SCR system, urea is pyrolyzed to generate ammonia and NOx in exhaust gases is reduced by the generated ammonia. The ammonia is occluded in a catalyst carrier and reacts with and thereby reduces NOx in an exhaust gas passing through the catalyst carrier.
WO2005/063653 discloses a honeycomb structure used as a catalyst carrier in such a system. The disclosed honeycomb structure is produced by combining honeycomb units. Each of the honeycomb units is made by mixing γ-alumina, ceria, zirconia, zeolite, and the like with inorganic fibers and a binder for improving the strength, molding the mixture into a honeycomb shape, and firing the molded body. Thus, the disclosed honeycomb structure has improved strength that is an important factor for a catalyst carrier used for vehicles.
The entire contents of WO 2005/063653 are incorporated herein by reference.